Existing active horizontal guidance controllers use a simple control strategy that utilizes only local gap information to hold the elevator within a predetermined operating envelope, essentially a predetermined acceptable range in values of the position, velocity, and acceleration of the elevator. For controllers that are electromagnet-based, so-called active magnetic guidance (AMG) controllers, the electromagnetic actuators that produce forces in a particular direction at a particular guide-head use only the gap information for that direction at that particular guide-head. Since the forces produced by an actuator for one direction at one guide-head can produce motion at another guide-head or at the same guide-head in a transverse direction, when only information local to an actuator is taken into account by the controller, one actuator can interfere with another.
The controllers are often of the "proportional integral derivative" (PID) type. For these controllers, the control information utilized by the controller in determining actuator forces consists of the gap (determined from the position of the guide-head relative to the rail), the absolute velocity of the guide-head, and the integrated gap over time. Such a controller uses sensors to directly measure guide-head acceleration and gap, and infers velocity of the guide-head from its integrating acceleration over time. For each guide-head, acceleration and gap are usually sensed in two directions, called here the x and y-directions, which are mutually perpendicular and also both perpendicular to the direction of the hoistway, taken here to be in the z-direction.
In one embodiment of a global controller designed to use nonlocal information, a related patent application ("Active Magnetic Guidance for Elevators," filed Aug. 18, 1994, under U.S. Ser. No. 08/292,660) suggested the use of a "coordinated controller" in which gap information was expressed in terms of a set of coordinates especially suitable for the problem of describing the elevator cab motion. However, that invention did not base control of the elevator on knowledge of the dynamics of the elevator; the control law there is not model-based, and is not designed to avoid actuator-actuator interference.